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Lovelock and Watson developed the Daisyworld computer
simulation model to prove that purposeful action by the
biosphere is not required for temperature regulation, but
instead that processes of natural selection are sufficient
to accomplish the task. Although
the earth is too complex a system to be modelled
mathematically, Daisyworld is a simplified model in which
much of the complexity has been stripped away and only the
fundamental relationships and characteristics are retained.
The hypothetical Daisyworld orbits a sun whose radiant
energy is slowly increasing. Daisyworld is seeded with two
varieties of daisy as its only life forms: black daisies and
white daisies. White petalled daisies reflect light, while
black petalled daisies absorb light. At the beginning of the
simulation, the sun's rays are weak and Daisyworld is too
cold to support any life. Its surface is barren and grey. As
the luminosity of the sun's rays increases, germination of
black daisies becomes possible. Because black daisies absorb
more of the sun's radiant energy, they are able to increase
their individual temperatures to healthy levels on the still
cool surface of Daisyworld. As a result they thrive and the
population soon grows large enough to increase the average
temperature of Daisyworld. As the surface heats up it
becomes more habitable for white daisies whose competing
population grows to rival the black daisy population. As the
two populations reach equilibrium, so does the surface
temperature of Daisyworld, which settles on a value most
comfortable for both populations. The second phase of the
simulation documents what happens when the sun's luminosity
continues to increase, heating the surface of Daisyworld
beyond a comfortable range for the daisies. This temperature
increase causes the white daisies, who are better able to stay
cool because of their high albedo, or ability to reflect
sunlight, to gain a selective advantage over the black
daisies. White daisies begin replacing black daisies, which
has a cooling effect on Daisyworld. The result is that
Daisyworld's surface temperature remains habitable, in fact
almost constant, even as the luminosity of the sun continues
to increase. In the third phase of the simulation, the sun's
rays have grown so powerful that soon even the white daisies
cannot survive. At a certain luminosity the
population crashes, and the barren, grey surface of
Daisyworld, no longer able to reflect the sun's rays, rapidly
heats up. At this point in the simulation solar luminosity
is programmed to decline, retracing its original path to the
initial value. Even as it declines to levels that
previously supported vast populations of daisies in the third
phase, no daisies are able to grow because the surface of
barren, grey Daisyworld is still far too hot. Eventually the power of
sun's rays decrease to a more comfortable level,
allowing white daisies to grow, and the planet begins cooling.
Later extensions of the simulation include rabbits,
foxes and other species. One of the findings of these
simulations is that a larger number of species improves the
temperature regulation.
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